I. Field of the Invention
The present invention relates to multi-braided exterior tubes having a lubricious inner layer, reinforcing layers and polymeric matrix layer. The present invention is used for a variety of medical devices such as intravascular devices, and catheters, such as guide catheters, angioplasty catheters, stent delivery devices, angiographic catheters, neuro catheters, and the like.
II. Discussion of the Prior Art
Tubes have been used for a variety of medical devices. Tubes have been used as a sheath component for catheters or exterior tubes for delivery devices. Several types of catheters having a sheath component are utilized for intravascular treatment. Examples of intravascular catheters include guide catheters, angioplasty catheters, stent delivery devices, angiographic catheters, neuro catheters, and the like.
Guiding catheters typically have preformed bends formed along their distal portion to facilitate placement of the distal end of the guiding catheter into the ostium of a particular coronary artery of a patient. In order to function efficiently, guiding catheters should have a relatively stiff yet flexible main body portion. The stiff main body portion gives the guiding catheter greater longitudinal stiffness which provides sufficient “pushability” to allow the guiding catheter to be inserted percutaneously into a peripheral artery, moved and rotated in the vasculature to position the distal end of the catheter at the desired site adjacent to a particular coronary artery. However, it has sufficient bending flexibility so that it can track over a guidewire and be maneuvered through a tortuous path to the treatment site. In addition, a soft distal tip at the very distal end of the catheter may be used to minimize the risk of causing trauma to a blood vessel while the guiding catheter is being moved through the vasculature to the proper position. Such a soft tip is described in U.S. Pat. No. 4,531,943. In addition, the inner surface of the guiding catheter should be lubricious to facilitate movement of guidewires, balloon catheters and other interventional medical devices therethrough.
In that the path taken by intravascular catheters is sometimes tortuous, it is important that an intravascular catheter provide torsional stiffness so that the torque be transmitted to the distal end in a smooth, controllable fashion. Moreover, the catheter should have sufficient longitudinal strength so as not to kink or fold as it is advanced or withdrawn through the vascular system. It should also possess a lubricious core lumen to facilitate passage of a guidewire or possibly another catheter or device therethrough.
Intravascular catheters may also be used as an outer sheath or exterior tube for a stent or stent-graft delivery device. In this application the outer sheath needs to provide sufficient bending flexibility to allow the device to be tracked through the anatomy as well as longitudinal stiffness to provide pushability and to minimize elongation. In the case of a self-expanding stent, the outer sheath must maintain the stent-graft in the compressed state. The stent exerts outward force against the inside of the outer sheath. Over time, the stent can form impressions in the inner surface of the sheath. During deployment a tensile deployment force is applied to the outer sheath to overcome the frictional forces between the stent and the inside of the outer sheath further causing the outer sheath to longitudinally deform. Typically, longer stents result in a higher deployment force, and a more extensive stretching of the exterior tube. Eventually, a threshold is reached where the outer sheath is not capable of sustaining the tensile loads without sustaining permanent deformation. When this threshold is reached, this typically results in an inability to deploy the stent. Thus, the lengths of the stents or stent-grafts that are offered on a particular delivery system can be limited by the tensile strength or stiffness of an outer sheath of the delivery system.
A braided reinforcement layer incorporated into an outer sheath provides greater longitudinal tensile strength, compressive stiffness and longitudinal stiffness, yet the braid structure provides flexibility as needed for the intravascular environment in which it is used. But the reinforcement layer must also not add significant thickness to the diameter of the catheter which must be easily maneuverable within the vascular system. It is advantageous to have catheters or delivery systems which are as small as possible to reach into smaller vessels, and cause less trauma to the patient. Some attempts have been made to offer the advantages of one reinforcing layer such as those found in U.S. Pat. No. 6,019,778 to Wilson et al., U.S. Pat. No. 5,836,926 to Peterson, et al., and U.S. Pat. No. 6,042,578 to Dinh et al. all of which are incorporated herein. However, none of these patent have suggested using more than one layer of reinforcement.
It is also a desirable feature of certain intravascular catheters that it possesses a relatively large lumen to maximize the available volume available for implantable components or fluids, such as radiopaque contrast fluid to be injected therethrough and out the distal end so that the area of the vascular system under investigation can be viewed fluoroscopically.
A desirable sheath for the above-mentioned utility has a relatively small O.D. and a relatively large I.D. which dictates a relatively thin wall. Further the outer sheath must provide the desired longitudinal stiffness providing adequate “pushability” and tensile strength characteristics, and radial torsional stiffness, to allow for placement of the device in the narrow, tortuous environment of the intravascular system without injury to the patient. The outer sheath must provide a balance between increased longitudinal stiffness and bending flexibility to provide strength yet flexibility for movement within a body lumen.